Tag Archives: supramolecular polymer

J. Phys. Chem. B纪念de Gennes

JPCB封面

JPCB封面

J. Phys. Chem. B出了一期de Gennes纪念专刊。王鸿飞在博客里提到了这件事，但他转而联系到了非科学的话题。

de Gennes的去世是一件大事，纪念事件不少。我前年在Nature Network上面纪念过他一回，以我当时的水平简单介绍了一些软物质现象和原理。

大科学家的的传记和事迹，多数会在相关领域的期刊的讣告和纪念专刊上找得到。这次J. Phys. Chem. B上就有一篇de Gennes的传记，写得比较平实，完成任务式。但里面有一句话挺有意义：

He started studying disordered systems–polymers, colloids, surfactants, micromulsions–that were not considered noble enough by physicists and thus were left to chemists and physical chemists to research.

我联想到在科苑星空BBS的物理版上，有很多同学看待自己的专业是带有一种非理性的崇拜的，具体表现为对粒子物理的钟爱，同时对凝聚态物理的鄙视。他们认为，物理学是用来炫耀一个人的pure mind和IQ的，凝聚态物理对他们来说太dirty。这些错觉也许是学生式的肤浅造成的。科学的趣味并不存在于这一层。

像de Gennes这样的所谓“牛人”，其中一方面“牛”在你摆脱不了他。从高分子科学中，有很长一段时间，人们摆脱不了Flory——他一个平均场就几乎把高分子的整个理论占了个遍。而到了60年代之后，大家发现de Gennes也有点摆脱不了了。高分子的浓稠体系和缠结现象自然摆脱不了他，相变离不了他，液晶离不了他，colloid离不了他，连wetting也离不了他。你在查文献的时候，回溯啊回溯，总回发现要说一句“怎么又是de Gennes”。

纪念专刊的常规做法是发表该人物涉足过的各相关领域的最新research paper。但是一个issue的篇幅是有限的，最终出来的paper体现了该期刊的Editor的取舍，即他对“什么能代表该领域最新动态”的个人理解。让我喜悦的是，我正在从事的非线性流变学研究以及LAOS方法恰好在这期里占了一篇paper（J. Phys. Chem. B 2009, 113, 3799-3805）。该文章理论上探讨了一种特殊的非线性现象——负法向力和应力硬化现象，并采用了MITLaos分析软件。MITLaos软件是由MIT的LAOS研究活跃分子McKinley组开发的Matlab插件，我前几个月也搞了一份准备用在我的研究中。这篇文章是我看到的第一篇用MITLaos软件的Paper。

这一期另一篇让我感兴趣的文章（J. Phys. Chem. B 2009, 113, 3920-3931）是关于高分子流体中发生的自组装现象的研究。自组装如果在高分子介质内发生，将对高分子相平衡产生影响。其实，在一高分子相中引发另一高分子的聚合所导致的相分离（namely, Polymerization-Induced Phase Separation）早就为人所熟悉，常规塑料HIPS（高抗冲聚苯乙烯）就是一个例子。新的兴趣点来自把Polymerization改成Self-assembly。把“聚合”换成“自组装”的思想早就体现在目前比较热门的所谓“超分子聚合物”（supramolecular polymers）研究中了，但是这篇paper所代表的是一个更加宏大的思想，把“超分子聚合物”参照传统高分子物理学科的内容——拓展到溶液、相变、转变和力学性能等等，“橡胶增韧塑料”和“塑料增强橡胶”等等老话题又有了新的理论内涵。超分子化学把“键”这个化学基本概念乘以了1.5，整个化学的研究可能就要乘以10。

与Angew. Chem.作者的一次交流

在新看到的Early View版的Angew. Chem. Int. Ed.上看到一篇Highlights文章，有感，就给作者发了个email。以下是我email的内容和他的回复。

Prof. Craig,

I have read your recently published Highlight article on ionic network materials. The paper from which you started your discussion (JACS 130:9648) described two networks that, in the view point of polymer gels, both have an average molecular weight between crosslinks of only ~1500. The materials in the works by D. W. Armstrong et al have lower values of chain lengths. That’s why it is so interesting that the material can show “polymer-like” behavior in the apparently solid state, without sufficient “configuration number” available molecularly. The dramatic effect of changing the anion from flexible EDTA4- to rigid H2tp4- on the moduli is also interesting. You have proposed a series questions in the end of your Highlight article, among which I think the most straightforward is how “polymer-like” this class of materials are, and where the “polymer-like” behaviors come from. Even in the classic field of polymer physics, the current molecular theories still cannot provide prudent and confident comfirmation of the origins and dynamics of the bulk properties, though rheology has pratically established various generally accepted criteria for describing and understanding chain dynamics and networks. More rheological study on ionic liquid materials may possibly set them inside the framework of and provide new tests on currently gelation and gel theories, with their structural uniqueness and accuracy compared with the high molecular weight polymer counterparts.
—
Cheers,

Andrew Sun

Thanks, Andrew.  I completely agree.  Although the authors of the original paper discuss their results in the context of supramolecular polymer networks, it is not clear that this will prove to be the most appropriate framework for discussing their properties, but the empirical results are potentially useful and interesting on their own.  Frankly, of it all the fact that the solid-like porphyrin-based materials are reported to have some elasticity is the observation I would have been least likely to expect, although the authors provide fairly limited characterization of those materials.

I like very much your statement that “current molecular theories cannot provide…confident confirmation of the origins and dynamics of the bulk properties”, and I actually think that there are wonderful opportunities created by these supramolecular approaches to polymer science, because they offer the opportunity for very specific control of very specific macromolecular dynamics and therefore to test some theories of polymer physics. While these ionic systems are interesting, however, it is not clear to me that they are easily suited to such a pursuit. My sense is that the multi-body interactions inherent in densely coulombic systems create quite a complex situation that is not easily deconvolved.

Best,

SC